spore: profile
id: indium
spore_version: 0.2
family: low-melting-metals-and-solders
name: Indium
abbreviation: In
role: soft low-melting metal for indium tin oxide coatings, solders, seals and bump bonds
category: metals
type: heavy-metals
summary: |
  Indium is the element In (atomic number 49), a soft, ductile, silvery-white metal that melts at 156.6 degC. Most of it is used as indium tin oxide (ITO), a transparent conductive coating for flat-panel displays and touchscreens (USGS). Foil from one supplier has a density of 7.3 g/cm3 at 20 degC, a thermal conductivity of 81.8 W/(m K) at 0 to 100 degC and a tensile modulus of 10.6 GPa. The metal is softer than tin, with a Mohs hardness of 1.2 (WebElements), and it forms a thin indium oxide crust in room-temperature air, which the NASA Goddard report on bump bonding says must be removed before a good electrical joint is made.
best_for: 'Soft, low-melting metal for seals, solders and bonds: melting point 156.6 degC and ductile enough to form a wire O-ring (NASA)'
weakest_at: 'Strength and cost: tensile strength of 2.6 to 4.5 MPa in the supplier foil, and a 2025 U.S. price of about 370 dollars per kg (USGS)'
identity:
  formula: In (element, atomic number 49, group 13); high-purity foil sold at 99.8 % to 99.999 % In
  cas: 7440-74-6
  source: pubchem-in
  where: Identifiers section of the PubChem record (CID 5359967, CAS 7440-74-6); purity range from the Goodfellow indium foil page
tags:
  applications:
    - electronics-and-chips
    - thermal-control
    - mechanisms
properties:
  - benchmark: density
    label: Density of indium (PubChem)
    value: 7.31
    unit: g/cm3
    scope: material
    conditions:
      temperature: 20 degC
    method: Value printed in the density section of the PubChem record
    status: ground
    source: pubchem-in
    where: Density section, entry 7.31 g/cu cm at 20 degC
  - benchmark: density
    label: Density of indium foil (Goodfellow)
    value: 7.3
    unit: g/cm3
    scope: material
    conditions:
      temperature: 20 degC
      form: foil, 99.8 % to 99.999 % In (as sold)
    method: Value printed on the supplier foil page
    status: ground
    source: goodfellow-in
    where: Physical Properties table, Density row (7.3 at 20 degC)
  - benchmark: density
    label: Density of solid indium (WebElements)
    value: 7310
    unit: kg/m3
    scope: material
    conditions:
      form: solid
      temperature: not stated on the page
    method: Value printed on a reference-database physical properties page
    status: ground
    source: webelements-in
    where: Density properties, Density of solid row (7310 kg m-3)
  - benchmark: melting_point
    label: Melting point of indium (Goodfellow)
    value: 156.6
    unit: degC
    scope: material
    conditions:
      form: foil, as sold
    method: Value printed on the supplier foil page
    status: ground
    source: goodfellow-in
    where: Thermal Properties table, Melting point row (156.6)
  - benchmark: melting_point
    label: Melting point of indium (PubChem)
    value: 156.6
    unit: degC
    scope: material
    conditions:
      pressure: not stated
    method: Value listed in the melting point section of the PubChem record
    status: ground
    source: pubchem-in
    where: Melting Point section, entry 156.6 degC (the record also lists 156.61 degC)
  - benchmark: boiling_point
    label: Boiling point of indium
    value: 2080
    unit: degC
    scope: material
    conditions:
      pressure: 760 mmHg
    method: Value listed in the boiling point section of the PubChem record
    status: ground
    source: pubchem-in
    where: Boiling Point section, entry 2080 degC @760 [mm Hg]
  - benchmark: latent_heat_of_fusion
    label: Latent heat of fusion of indium
    value: 28.5
    unit: J/g
    scope: material
    conditions:
      form: foil, as sold
    method: Value printed on the supplier foil page
    status: ground
    source: goodfellow-in
    where: Thermal Properties table, Latent heat of fusion row (28.5)
  - benchmark: thermal_conductivity
    label: Thermal conductivity of indium foil (Goodfellow)
    value: 81.8
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: 0 to 100 degC
      form: foil, as sold
    method: Value printed on the supplier foil page
    status: ground
    source: goodfellow-in
    where: Thermal Properties table, Thermal conductivity row (81.8 at 0-100 degC)
  - benchmark: thermal_conductivity
    label: Thermal conductivity of indium (WebElements)
    value: 82
    unit: W/(m·K)
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a reference-database physical properties page
    status: ground
    source: webelements-in
    where: Heat and conduction, Thermal conductivity row (82 W m-1 K-1)
  - benchmark: specific_heat
    label: Specific heat of indium foil (Goodfellow)
    value: 234
    unit: J/(kg·K)
    scope: material
    conditions:
      temperature: 25 degC
      form: foil, as sold
    method: Value printed on the supplier foil page
    status: ground
    source: goodfellow-in
    where: Thermal Properties table, Specific heat row (234 at 25 degC)
  - benchmark: cte
    label: Coefficient of thermal expansion of indium foil (Goodfellow)
    value: 24.8
    unit: ppm/K
    scope: material
    conditions:
      temperature: 0 to 100 degC
      unit_in_source: x10-6 K-1
      form: foil, as sold
    method: Value printed on the supplier foil page
    status: ground
    source: goodfellow-in
    where: Thermal Properties table, Coefficient of thermal expansion row (24.8 at 0-100 degC)
  - benchmark: cte
    label: Coefficient of linear thermal expansion (WebElements)
    value: 32.1
    unit: ppm/K
    scope: material
    conditions:
      unit_in_source: x10-6 K-1
      temperature: not stated on the page
    method: Value printed on a reference-database physical properties page
    status: ground
    note: Differs from the supplier value of 24.8 ppm/K by about 30 %. The two pages give no common temperature, so both are recorded and neither is preferred.
    source: webelements-in
    where: Heat and conduction, Coefficient of linear thermal expansion row (32.1 x 10-6 K-1)
  - benchmark: electrical_resistivity
    label: Electrical resistivity of indium foil (Goodfellow)
    value: 8.8
    unit: µΩ·cm
    scope: material
    conditions:
      temperature: 20 degC
      form: foil, as sold
    method: Value printed on the supplier foil page
    status: ground
    source: goodfellow-in
    where: Electrical Properties table, Electrical resistivity row (8.8 at 20 degC)
  - benchmark: superconducting_transition_temperature
    label: Superconducting critical temperature of indium
    value: 3.41
    unit: K
    scope: material
    conditions:
      form: foil, as sold
    method: Value printed on the supplier foil page
    status: ground
    source: goodfellow-in
    where: Electrical Properties table, Superconductivity critical temperature row (3.41)
  - benchmark: elastic_modulus
    label: Young's modulus of indium (WebElements)
    value: 11
    unit: GPa
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a reference-database physical properties page
    status: ground
    source: webelements-in
    where: Elastic properties, Young's modulus row (11 GPa)
  - benchmark: elastic_modulus
    label: Tensile modulus of indium foil (Goodfellow)
    value: 10.6
    unit: GPa
    scope: material
    conditions:
      material_condition: polycrystalline
    method: Value printed on the supplier foil page
    status: ground
    source: goodfellow-in
    where: Mechanical Properties table, Tensile modulus row (10.6 GPa)
  - benchmark: bulk_modulus
    label: Bulk modulus of indium foil (Goodfellow)
    value: 35.3
    unit: GPa
    scope: material
    conditions:
      material_condition: polycrystalline
    method: Value printed on the supplier foil page
    status: ground
    source: goodfellow-in
    where: Mechanical Properties table, Bulk modulus row (35.3 GPa)
  - benchmark: poissons_ratio
    label: Poisson's ratio of indium foil (Goodfellow)
    value: 0.45
    unit: '-'
    scope: material
    conditions:
      material_condition: polycrystalline
    method: Value printed on the supplier foil page
    status: ground
    source: goodfellow-in
    where: Mechanical Properties table, Poisson's ratio row (0.45)
  - benchmark: ultimate_tensile_strength
    label: Tensile strength of indium foil (Goodfellow)
    value: 2.6
    value_high: 4.5
    bound: range
    unit: MPa
    scope: material
    conditions:
      material_condition: soft, as listed in the supplier table
    method: Range printed on the supplier foil page
    status: ground
    source: goodfellow-in
    where: Mechanical Properties table, Tensile strength row (2.6-4.5 MPa)
  - benchmark: mohs_hardness
    label: Mineral hardness, Mohs scale (WebElements)
    value: 1.2
    unit: '-'
    scope: material
    conditions:
      temperature: not stated on the page
    method: Value printed on a reference-database physical properties page
    status: ground
    source: webelements-in
    where: Hardnesses, Mineral hardness row (1.2)
  - benchmark: brinell_hardness
    label: Brinell hardness of indium (WebElements)
    value: 8.83
    unit: MN/m2
    scope: material
    conditions:
      test_conditions: not stated on the page
    method: Value printed on a reference-database physical properties page
    status: ground
    source: webelements-in
    where: Hardnesses, Brinell hardness row (8.83 MN m-2)
  - benchmark: vickers_hardness
    label: Vickers hardness of indium foil (Goodfellow)
    value: 10
    unit: kgf/mm2
    scope: material
    conditions:
      material_condition: polycrystalline
    method: Value printed on the supplier foil page
    status: ground
    source: goodfellow-in
    where: Mechanical Properties table, Hardness Vickers row (10 kgf mm-2)
  - benchmark: vapor_pressure
    label: Vapour pressure of indium at its melting point
    value: 1.14e-19
    unit: Pa
    scope: material
    conditions:
      temperature: at the melting point
    method: Value listed in the vapour pressure section of the PubChem record
    status: ground
    source: pubchem-in
    where: Vapor Pressure section, entry 1.14X10-19 Pa at melting point
corrosion:
  - environment: Room-temperature air
    headline: In room-temperature air, indium quickly forms a thin indium oxide (In2O3) crust that must be removed before a good electrical joint.
    effect: NASA Goddard's bump-bonding report says indium readily oxidizes in air at room temperature to form a thin In2O3 crust. The oxide resists rupture during bonding, which can cause poor adhesion and block electrical conduction. Ellipsometry on untreated indium gave a steady Delta of about 128, which the report links to the native oxide; a plasma treatment removed it, and the oxide regrows once the reduced surface leaves vacuum. The report gives no oxide thickness or growth rate.
    rating: moderate
    conditions:
      basis: NASA Goddard observation during flip-chip hybridization; cleanroom air
      thickness: not given in the source
    source: ntrs-mosaic
    where: Section 2.2 (Plasma Cleaning) and the ellipsometry discussion that follows
  - environment: Air at room temperature (supplier statement)
    headline: The supplier says the oxide layer protects indium without much loss of thermal or electrical performance.
    effect: Goodfellow states that indium forms a stable, self-passivating oxide layer and that this supports long-term reliability in sealed or exposed systems. The supplier page gives no test data, no thickness and no time scale, so this is recorded as a claim, not a measured result.
    rating: low
    conditions:
      basis: supplier product text, no test data
    source: goodfellow-in
    where: Product text, Indium foil description (self-passivating behaviour paragraph)
risks:
  hazards:
    - text: PubChem reports that the first GHS notification block for indium carries signal word Danger, with H302 (15.1 %), H312 (12.7 %), H315 (15.4 %) and H319 (13.2 %). It also says 18.6 % (69 of 371) of company reports do not meet GHS criteria. The record does not say which indium substance each notification covers.
      ghs:
        - H302
        - H312
        - H315
        - H319
      source: pubchem-in
      where: GHS Classification section, first block (ECHA C&L aggregated notifications, 371 reports)
    - text: A second PubChem GHS block for indium lists H303 (may be harmful if swallowed) and H372 (causes damage to organs through prolonged or repeated exposure), with signal word Danger.
      ghs:
        - H303
        - H372
      source: pubchem-in
      where: GHS Classification section, second block
    - text: The NIOSH excerpt in PubChem lists the exposure routes as inhalation, ingestion, and skin or eye contact. Symptoms include irritation of the eyes, skin and respiratory system, and possible liver, kidney, heart and blood effects. Target organs are listed as the eyes, skin, respiratory system, liver, kidneys, heart and blood.
      ghs: []
      source: pubchem-in
      where: Health Hazards section, NIOSH Pocket Guide excerpt (2024)
    - text: PubChem's human toxicity excerpts say that indium may damage the developing fetus and may damage the lungs. Higher exposures can cause pulmonary oedema, which can be delayed by several hours.
      ghs: []
      source: pubchem-in
      where: Human Toxicity Excerpts, long-term and short-term exposure entries
  failure_risks:
    - mode: Dust explosion of indium powder
      trigger: Indium in powder or granular form mixed with air
      consequence: PubChem's physical-dangers entry says a dust explosion is possible, and that finely dispersed particles form explosive mixtures in air.
      severity: moderate
      source: pubchem-in
      where: Physical Dangers and Fire Potential sections
    - mode: Leakage of an indium seal on rapid cooling
      trigger: Rapid cooling of a demountable indium seal, especially after repeated cycles
      consequence: NASA Ames notes that leakage frequently occurs under rapid cooling of indium seals. Its own test seals, flat indium/silver alloy rings in a stainless steel guard, were cooled rapidly by immersion and showed no detectable leak at any temperature, including 1.6 K after 13 mount and demount cycles.
      severity: moderate
      source: ntrs-seal-1989
      where: Introduction and results, NASA TM 102190 (1989)
    - mode: Oxide film blocks an electrical joint
      trigger: Indium exposed to room-temperature air before bonding, or a surface reduced but then returned to air
      consequence: The In2O3 crust resists rupture when bonding, and the report says it can block electrical conduction and inhibit a superconducting joint. The oxide regrows once a reduced surface is exposed to air again.
      severity: moderate
      source: ntrs-mosaic
      where: Section 2.2 (Plasma Cleaning)
  side_effects: []
  handling:
    - text: 'PubChem fire-prevention guidance for indium powder: no open flames, no sparks and no smoking. Use a closed system, dust-explosion-proof electrical equipment and lighting, and prevent dust from settling.'
      source: pubchem-in
      where: Fire Prevention section
    - text: PubChem's fire-fighting excerpt, taken from ERG Guide 170 for metal powders, says not to use water, foam or CO2 on metal fires because water can generate hydrogen. It recommends dry sand, graphite powder or a dry sodium-chloride-based powder. The excerpt is a generic guide for metal powders, not an indium-specific test.
      source: pubchem-in
      where: Fire Fighting section, ERG Guide 170 excerpt
  mitigations:
    - text: The NASA Goddard team cleaned indium surfaces in a plasma of nitrogen-rich, reducing gas just before bonding, which removed the native oxide and gave a good electrical joint.
      source: ntrs-mosaic
      where: Section 2.2 (Plasma Cleaning)
uses:
  - application: electronics-and-chips
    device: Indium tin oxide (ITO) transparent conductive coatings in flat-panel displays
    example: USGS says ITO production continued to account for most global indium consumption, mainly for liquid crystal displays. Estimated U.S. consumption of refined indium was 220 tons in 2025.
    source: usgs-mcs2026-indium
    where: Domestic Production and Use paragraph and Salient Statistics table
  - application: electronics-and-chips
    device: Indium phosphide substrates, lasers and photodetectors for fibre-optic networks
    example: USGS says indium phosphide (InP) substrates are used in 5G fibre-optic networks, and that InP lasers and receivers send data over fibre lines. It also says InP is used in high-speed photodetectors and laser diodes.
    source: usgs-mcs2026-indium
    where: Events, Trends, and Issues paragraph
  - application: electronics-and-chips
    device: Indium bump bonds that join detector arrays to silicon readout chips (far-infrared detector model)
    example: NASA Goddard built a 32 by 40 pixel detector model in which 10 µm of indium was deposited by lift-off on the readout chip's under-bump metal. When hybridized, the indium cold-welds to the detector's molybdenum nitride. The report is a ground demonstration with no flight heritage.
    source: ntrs-mosaic
    where: Section 2.1 (Fabrication)
  - application: mechanisms
    device: Flat indium/silver alloy seal in a stainless steel guard for demountable cryogenic joints (ground test, not flown)
    example: NASA Ames leak-tested two all-metal demountable seals of this design at 300 K, 77 K, 4.2 K and 1.6 K, with no detectable leak above the helium background. The report notes that indium has been used in demountable cryogenic seals because it is easy to form into an O-ring from wire.
    source: ntrs-seal-1989
    where: Introduction, NASA TM 102190 (1989)
  - application: thermal-control
    device: Indium foil as a thermal interface between surfaces in electronics
    example: The supplier describes indium foil as a thermal interface material that fills microscopic gaps. The page gives no thermal-resistance value, so this is a product claim, not a measured result.
    source: goodfellow-in
    where: Product text, Indium foil description (thermal interface paragraph)
supply:
  - subject: Indium (refinery production)
    producers:
      - country: China
        share_percent: 70
        year: 2025
      - country: Republic of Korea
        share_percent: 16.4
        year: 2025
      - country: Japan
        share_percent: 5.9
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals
        listed: true
      - list: EU critical raw materials list (Commission page, 2023 assessment)
        listed: false
    recycling: 'USGS: indium is most commonly recovered from ITO scrap in Japan and the Republic of Korea. Recycling quantities were not available.'
    substitutes:
      - 'USGS: antimony tin oxide, carbon nanotube coatings, PEDOT, copper or silver nanowires, graphene and zinc oxide nanopowder have been developed or explored to replace ITO. Hafnium can replace indium in nuclear reactor control rod alloys.'
    source: usgs-mcs2026-indium
    where: World Refinery Production and Capacity table, 2025e column (world total 1,100 t). China 70 % is as printed in Events, Trends, and Issues; Korea and Japan shares are calculated by Space Mushroom (180 and 65 over 1,100); Recycling; Substitutes
    abundance: 0.25 ppm in the Earth's crust (USGS Professional Paper 1802-A, Table A1)
    notes: 'USGS: indium is most commonly recovered from zinc-sulfide ore, sphalerite, with indium content of zinc deposits from under 1 to 100 ppm (World Resources paragraph).'
  - subject: Refined indium imports to the United States
    producers:
      - country: Republic of Korea
        share_percent: 25
        year: 2024
      - country: Japan
        share_percent: 22
        year: 2024
      - country: China
        share_percent: 12
        year: 2024
      - country: Canada
        share_percent: 11
        year: 2024
    critical_lists: []
    source: usgs-mcs2026-indium
    where: Import Sources (2021-24) paragraph; the year is the end of the 2021 to 2024 period as printed. The United States has no indium refinery output in 2025 (Salient Statistics).
  - subject: Trade restriction on indium exports from China
    demand: 'USGS: in February 2025 China''s Ministry of Commerce put new export restrictions on several critical minerals, including indium. Asian Metal reported that exports of unwrought indium fell 72 % year on year from September 2024 to September 2025.'
    critical_lists: []
    source: usgs-mcs2026-indium
    where: Events, Trends, and Issues paragraph
documents:
  - title: 'USGS Mineral Commodity Summaries 2026: Indium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-indium.pdf
    year: 2026
  - title: 'PubChem compound record for indium (CID 5359967): density, melting and boiling points, GHS and NIOSH excerpts'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Indium
    year: 2026
  - title: 'WebElements: indium physical properties'
    type: database
    url: https://www.webelements.com/indium/physics.html
  - title: Goodfellow indium foil, 99.8 % to 99.999 %, properties table
    type: datasheet
    url: https://www.goodfellow.com/eu/indium-foil-group
  - title: NIST Atomic Weights and Isotopic Compositions for All Elements, indium
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=In&all=all&ascii=html
  - title: USGS Professional Paper 1802-A, Table A1, crustal abundances
    type: report
    url: https://pubs.usgs.gov/pp/1802/a/pp1802a.pdf
    year: 2017
  - title: 'NASA Ames TM 102190: Performance of All-Metal Demountable Cryogenic Seals at Superfluid Helium Temperatures'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19890013479/downloads/19890013479.pdf
    year: 1989
  - title: 'NASA Goddard: Enabling large focal plane arrays through mosaic hybridization'
    type: report
    url: https://ntrs.nasa.gov/api/citations/20130013418/downloads/20130013418.pdf
  - title: 'Congressional Research Service IF13145: USGS Critical Minerals List (final 2025 list)'
    type: report
    url: https://www.everycrsreport.com/files/2026-01-07_IF13145_e385924a2f20b8b1460afc40322d4137f1956556.pdf
    year: 2026
gaps:
  - No flight, vacuum, outgassing, atomic oxygen, UV or radiation data for indium in space were found in any fetched source. The seal and bump-bonding sources are ground tests.
  - Tensile strength, yield strength and elongation are from one supplier page only. Its material condition is printed as soft, but the page does not say which temper or purity each row refers to.
  - 'The coefficient of thermal expansion differs between sources: 24.8 ppm/K (supplier, 0 to 100 degC) and 32.1 ppm/K (WebElements, temperature not stated). Both are recorded and neither is preferred.'
  - WebElements prints electrical resistivity as 8 x 10 to the power -8 ohm m, with a special minus sign that the value check could not match, so that row is left out. The supplier value of 8.8 µΩ·cm at 20 degC is recorded instead.
  - 'Two entries in the PubChem record were left out as not credible: 1.6 MPa tensile strength and 291 ohm m electrical resistivity, which sit in a mixed list of other experimental values.'
  - Latent heat of fusion and superconducting critical temperature are not in spores/property-canon.yaml and are used under the names given in the benchmark field.
  - Corrosion rates in water, salt spray, acids and seawater were not found in a fetched source. PubChem gives only solubility (insoluble in water, soluble in acids).
  - No supplier safety data sheet for indium was read in this run. Hazard data rest on the PubChem summary and the NIOSH excerpt it quotes.
  - No UNS, ASTM, EN or other grade designation for indium was found in a fetched source.
  - 'The USGS gives the 2025 refined price three ways: about 350,000 dollars per ton in the summary, 370 dollars per kg in the table and 390 dollars per kg in the text. None of the three is used as a property value.'
  - The EU critical raw materials list on the Commission page does not include indium. That page reflects the 2023 assessment and may not match the 2024 regulation cited in the lithium profile.
  - The Wikipedia article was used only for history and the zinc-ore origin. Its values are not used.
  - No photograph or diagram of indium was fetched in this run, so the media list is empty.
sources:
  usgs-mcs2026-indium:
    title: 'Mineral Commodity Summaries 2026: Indium (U.S. Geological Survey)'
    id: USGS MCS 2026, February 2026, prepared by Rob Crangle
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-indium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  pubchem-in:
    title: 'PubChem compound record: Indium (CID 5359967), including GHS, NIOSH and ERG excerpts'
    id: CID 5359967; CAS 7440-74-6; PubChem REST pug_view JSON
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/5359967/JSON
    year: 2026
    kind: database
    license: PubChem (NCBI), public domain; sections attributed to ECHA, NIOSH and ERG
  webelements-in:
    title: 'WebElements: Indium - 49 In, physical properties (Mark Winter, University of Sheffield)'
    url: https://www.webelements.com/indium/physics.html
    kind: database
    license: WebElements, cited not reproduced
  goodfellow-in:
    title: Goodfellow indium foil, 99.8 % to 99.999 %, product properties
    id: CAS 7440-74-6; Goodfellow product page, Properties table
    url: https://www.goodfellow.com/eu/indium-foil-group
    kind: datasheet
    license: supplier product page, cited not reproduced
  nist-in-weights:
    title: NIST Atomic Weights and Isotopic Compositions for All Elements, indium (In)
    id: standard atomic weight 114.818(1)
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=In&all=all&ascii=html
    kind: database
    license: US government data
  pp1802a-crust:
    title: 'Critical Mineral Resources of the United States: An Introduction (USGS Professional Paper 1802-A), Table A1'
    id: USGS PP 1802-A
    url: https://pubs.usgs.gov/pp/1802/a/pp1802a.pdf
    year: 2017
    kind: report
    license: public domain (USGS)
  ntrs-seal-1989:
    title: Performance of All-Metal Demountable Cryogenic Seals at Superfluid Helium Temperatures (NASA Technical Memorandum 102190, Ames Research Center)
    id: NTRS 19890013479
    url: https://ntrs.nasa.gov/api/citations/19890013479/downloads/19890013479.pdf
    year: 1989
    kind: report
    license: public domain (NASA)
  ntrs-mosaic:
    title: Enabling large focal plane arrays through mosaic hybridization (NASA Goddard Space Flight Center)
    id: NTRS 20130013418
    url: https://ntrs.nasa.gov/api/citations/20130013418/downloads/20130013418.pdf
    kind: report
    license: public domain (NASA)
  crs-if13145:
    title: 'Congressional Research Service IF13145: USGS Critical Minerals List, final 2025 list of 60 minerals'
    id: IF13145, updated 2026-01-07
    url: https://www.everycrsreport.com/files/2026-01-07_IF13145_e385924a2f20b8b1460afc40322d4137f1956556.pdf
    year: 2026
    kind: report
    license: public domain (CRS)
  ec-crm:
    title: Critical raw materials (European Commission, critical raw materials list and 2023 assessment)
    url: https://single-market-economy.ec.europa.eu/sectors/raw-materials/areas-specific-interest/critical-raw-materials_en
    kind: web
    license: European Commission web page
  wiki-in:
    title: Indium, Wikipedia (history, naming and zinc-ore origin only)
    url: https://en.wikipedia.org/wiki/Indium
    kind: web
    license: CC BY-SA 4.0, linked not reproduced
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 23
  unreachable: 1
  caveats: 4
  note: 'Values were read by an AI assistant on 2026-10-26 from the pages and PDFs named in each entry (USGS text extracted from the PDF; NASA reports from the NTRS PDFs; PubChem values from its JSON record). Unreachable: the Indium Corporation sealing page (blocked) and the USGS critical-minerals page (403); the list status comes from the CRS report. Caveats: the CTE values disagree between sources; the PubChem density and melting values carry no test conditions; the GHS notifications do not say which indium substance they cover; the Korea and Japan refinery shares are calculated.'
story:
  recipe:
    line: Indium is a single element (In, atomic number 49, group 13). Most of it is recovered as a by-product of zinc. Wikipedia and the USGS say it comes mainly from zinc-sulfide ore, sphalerite, and is refined from zinc residues. The USGS summary gives production statistics but not the refining route, so the process is stated only at that level.
    parts:
      - name: Indium
        symbol: In
        atoms: 1
        atomic_weight: 114.818
        role: The whole material. NIST gives the standard atomic weight as 114.818(1).
  risk_groups:
    - title: For people
      level: 1
      verdict: Hazard codes in PubChem, little toxicology data
      lead: PubChem's notifications mostly report irritation codes, and the NIOSH excerpt lists organ effects from exposure to indium compounds, so dust and fume should be avoided.
      points:
        - label: The metal in PubChem
          line: The first GHS block gives H302, H312, H315 and H319 with signal word Danger. A second block gives H303 and H372 (organ damage from repeated exposure). PubChem says 69 of 371 company reports do not meet GHS criteria. The record does not say which indium substance each report covers.
        - label: Organs and development
          line: NIOSH lists the eyes, skin, respiratory system, liver, kidneys, heart and blood as target organs. PubChem's excerpts say indium may damage the developing fetus.
    - title: If it fails
      lead: The failure routes in these sources are a dust explosion of powder, a leaking seal on rapid cooling, and an oxide film that blocks a joint.
      points:
        - label: Powder
          line: PubChem says indium powder can form an explosive dust cloud in air, so keep dust down and use dust-explosion-proof equipment.
        - label: Seals
          line: NASA Ames notes that indium seals often leak on rapid cooling. Its own indium/silver test seals showed no detectable leak at any temperature down to 1.6 K, after 13 mount and demount cycles.
        - label: Oxide
          line: NASA Goddard found that the native In2O3 crust blocks electrical contact unless it is removed, for example by plasma cleaning just before bonding.
    - title: Handling and storage
      points:
        - label: Fire
          line: For powder, PubChem calls for no open flames, no sparks, a closed system and dust-explosion-proof equipment. Its fire guidance warns against water on metal powder fires (ERG Guide 170).
        - label: Surfaces
          line: Cold-weld bonding needs a clean surface. Clean the metal just before it is joined, because the oxide returns when the reduced surface is exposed to air again.
  why: 'Indium is a soft, ductile metal that melts at 156.6 degC. It is made into thin foils, wires and coatings, and its main use is indium tin oxide, a transparent conductor for displays. It is also used in solders and in cryogenic seals, because it can be formed into an O-ring from wire and stays soft at low temperature. Its drawbacks are its low strength, its oxide film in air and its concentrated supply: China produces about 70 % of refinery output (USGS).'
  uses:
    - where: Flat-panel displays and touchscreens
      line: Indium tin oxide coatings took most global indium consumption. U.S. consumption of refined indium was 220 tons in 2025 (USGS).
    - where: Fibre-optic and 5G networks
      line: Indium phosphide substrates and devices are used in lasers and high-speed photodetectors for fibre-optic communications (USGS).
    - where: Far-infrared detector arrays
      line: NASA Goddard bonds indium bumps to join detector arrays to readout chips. The work is a ground demonstration, not a flight unit.
    - where: Cryogenic seals
      line: NASA Ames leak-tested indium/silver alloy seals from 300 K down to 1.6 K (superfluid helium). It is a ground test, not a flight result.
  can_do:
    - label: Melt low
      value: 156.6 degC melting point
      benchmark: melting_point
      line: Indium melts at 156.6 degC, printed by both the supplier and PubChem.
    - label: Stay soft
      value: 2.6 to 4.5 MPa tensile strength
      benchmark: ultimate_tensile_strength
      line: The supplier foil has a tensile strength of 2.6 to 4.5 MPa and a Mohs hardness of 1.2 (WebElements).
    - label: Carry heat
      value: 81.8 W/(m·K)
      benchmark: thermal_conductivity
      line: The supplier foil has a thermal conductivity of 81.8 W/(m·K) at 0 to 100 degC. WebElements gives 82 W/(m·K).
    - label: Weight
      value: 7.3 g/cm3
      benchmark: density
      line: Density is 7.3 g/cm3 at 20 degC (supplier) and 7.31 g/cm3 at 20 degC (PubChem).
  compare: Indium is a soft, low-melting metal. Its melting point of 156.6 degC is low, and its tensile strength is far below that of structural alloys. The sources disagree on thermal expansion (24.8 and 32.1 ppm/K), so read the rows as ranges. The profile does not rank indium against other metals.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Thermal conductivity
      benchmark: thermal_conductivity
    - label: Thermal expansion
      benchmark: cte
  handling:
    - Use dust control for powder and keep ignition sources away, because PubChem records an explosive dust hazard.
    - Clean the surface just before bonding or sealing, because the oxide returns in air.
    - Follow the PubChem hazard codes (H302, H312, H315, H319, H303, H372) when handling the metal.
    - Keep the seal cool and cool it slowly, because NASA Ames found leaks on rapid cooling.
  good_for:
    - 'Low melting point and soft metal: 156.6 degC melting point, and a wire form that makes a cryogenic O-ring (NASA).'
    - 'Transparent conductive coatings: most indium goes into ITO for displays (USGS).'
  watch_out:
    - 'Low strength: tensile strength is 2.6 to 4.5 MPa in the supplier foil, and the Mohs hardness is 1.2.'
    - 'Oxide film: the In2O3 crust in air blocks electrical contact unless it is removed before bonding (NASA Goddard).'
    - 'Supply: China produces about 70 % of refinery output and cut its exports in 2025 (USGS).'
    - 'Thermal expansion: sources give 24.8 and 32.1 ppm/K.'
    - No flight, vacuum, outgassing, atomic oxygen or radiation data were found in this run.
  verdict: Indium is a soft, low-melting metal that is used mostly in transparent conductive coatings, with smaller roles in solders, cryogenic seals and bump bonds. Its weak points are its low strength, its oxide film in air, and its supply, which is concentrated in China. The profile has no flight or space-exposure data, so it can say what indium does on the ground but not how it behaves in orbit.